Ahuna Mons is a strange feature. It rises sharply from the cratered landscape, towering some 3 miles (5 km) on its steepest side. Pointing to a combination of characteristics, researchers are convinced that Ahuna Mons is volcanic. Its summit is cracked like those of volcanic domes seen on other worlds, such as Mars, Venus, and Earth. The mountain’s flanks appear to have been scored by rockfalls. Volcanic domes on terrestrial planets tend to form a brittle shell at the summit, which fractures and produces similar debris trails on their flanks.
Everything about Ahuna Mons indicates that the mountain is geologically young. Ceres has no atmosphere to protect it from meteor impacts, so much of its surface is weathered by the constant drizzle of micrometeorites, resulting in rounded hills and valleys. But Ahuna Mons shows sharp definition with few craters, suggesting it hasn’t experienced as much weathering. A final clue to its youth is its color: Ice and rock surfaces tend to darken over time thanks to constant solar radiation, but the dome is one of the brightest regions on Ceres.
Researchers estimate the age of the summit to be between 70 million and 240 million years old. The massif may have risen quite quickly, building to its current altitude of 13,000 feet (3,965 m) in just a few hundred to a few hundred thousand years. The idea that it might have reached that height so quickly inspires scientists like Rayman. “Even a few hundred thousand years for a structure that’s 13,000 feet high, that’s pretty fast,” he says. “Not only that: The structure is more than 70 million years old, and it’s still standing with impressively steep slopes.”
It is unclear whether Ahuna Mons still erupts cryolavas (most likely thick, muddy water). In light of its potential for geologic activity, researchers began searching Ceres’ surface for other evidence of past volcanism, but the search was difficult. Most of the world’s volcanic activity seems to have occurred hundreds of millions of years ago, and it may stretch back as far as 2 billion years. Time, impacts, radiation, and micrometeorites have nearly erased many of the ancient eruptions’ fingerprints.